Pat chicken dry and place in a sealable plastic bag or glass container. Add olive oil, maple syrup, mustard, garlic, salt and pepper and toss to coat. Seal bag/container and let marinate in the fridge for at least 1 hour.
While the chicken is marinating, prepare your vegetables for grilling. Wash and slice radishes and potatoes and place in a medium-sized mixing bowl, cutting larger pieces in half. Drizzle with olive oil and toss to coat. Transfer to foil and fold into a packet and seal.
Next, wash and trim asparagus and place on a plate. Drizzle with olive oil and set aside.
Once ready to cook, preheat grill (or oven*) to 400ºF (200ºC).
Place foil packet over flame and set timer for 30 minutes. After first 10 minutes, transfer drumsticks to grill and cook for 20 minutes until crispy and the chicken is cooked to an internal temperature of 165º, turning halfway through. With 5 minutes remaining, place asparagus on grill over flame. Cook turning continuously just until asparagus starts to char and has turned a bright green.
Remove chicken, foil packet and asparagus from grill. Transfer to serving plate, garnish with fresh tarragon and serve immediately.